The present invention relates to a method for the preparation of an aqueous emulsion of silicone, i.e. organopolysiloxane, or, more particularly, to a method for the preparation of an aqueous emulsion of an organopolysiloxane directly starting from organochlorosilanes.
As is well known, silicones or organopolysiloxane compositions are widely used in various fields utilizing their unique properties. When organopolysiloxanes are used as an antifoam agent, mold release agent, water repellent agent, polishing material and the like, the most widely accepted form of the silicone compositions is an aqueous emulsion which is prepared by emulsifying the organopolysiloxane in water in the presence of a surface active agent dissolved in the aqueous medium.
Needless to say, organopolysiloxanes are usually prepared by the hydrolysis of an organochlorosilane or a mixture of organochlorosilanes followed by the dehydration condensation of the silanols formed by the hydrolysis. Therefore, the usually undertaken way for the preparation of an aqueous emulsion of silicone is the secondary emulsifying processing of an organopolysiloxane prepared in advance. Therefore, an aqueous emulsion of silicone is prepared usually in a process including the steps for the hydrolysis of an organochlorosilane or chlorosilanes, dehydration condensation of the hydrolyzate to give an organopolysiloxane, purification of the organopolysiloxane and emulsification of the purified organopolysiloxane in water. Such a long sequence of process steps necessarily requires a high cost for the preparation of the emulsion. In addition, the rheological nature of the organopolysiloxane is limited in order to be satisfactorily emulsified in water. For example, an organopolysiloxane having an excessively high viscosity cannot be emulsified in water without dilution with a suitable organic solvent and resinous organopolysiloxanes can hardly be emulsified in water presenting great drawbacks to the practical application of silicone aqueous emulsions.
As viewed from the other side, organochlorosilanes are usually produced by the so-called direct method in which metallic silicon is reacted with a chlorinated hydrocarbon such as methyl chloride and chlorobenzene. In this case, various organochlorosilanes are concurrently produced while the monoorganotrichlorosilanes are produced in amounts over the industrial consumption thereof in comparison with the organochlorosilanes of the other types so that the monoorganotrichlorosilanes must be discarded as an industrial waste of nuisance. This situation led to a proposal of a method for the effective utilization of an organotrichlorosilane in which such an organotrichlorosilane is first converted into a corresponding trialkoxysilane which is then emulsified in water (see, for example, Japanese Patent Publication No. 52-12219). This method is, however, not always very advantageous from the standpoint of the production cost due to the expensive step of conversion of the trichlorosilane into the trialkoxylsilane in addition to the limitation in the selection of the surface active agent used in the emulsification of the trialkoxysilane.
Therefore, it has been eagerly desired to develop an inexpensive method for the preparation of an aqueous emulsion of silicone and, if possible, a method in which hitherto valueless monoorganotrichlorosilanes can be utilized as a starting material for an aqueous emulsion of a silicone composition.